1. Field of the Invention
The present invention relates to a bidirectional optical communication module using a single optical fiber, and in particular, to an improved bidirectional optical communication module using a single optical fiber which is capable of significantly improving an optical coupling operation between a bidirectional optical device into which a light receiving device is integrated into a light receiving semiconductor laser in a form of a single chip and an optical fiber.
2. Description of the Conventional Art
The optical communication module for an optical communication is divided into a transmission module and a receiving module for thereby implementing a transmitting and receiving operation using additional optical fiber. Recently, an optical transmission/receiving module in which an optical transmission portion and receiving portion are integrated into one package has been intensively studied. In this case, additional optical fiber is used. When only one optical fiber is used for thereby implementing a transmission and receiving operation instead of using additional optical fiber, the cost for installing the optical fiber is decreased. Therefore, it is possible to decrease the number of system parts for thereby economically implementing the optical communication system.
The optical transmission and receiving operations have been performed using one optical fiber. In order to implement a bidirectional optical communication which is capable of transmitting a transmission and receiving signal at the same time using one optical fiber, the bidirectional optical transmission/receiving module includes a Y-shaped light splitting waveguide device for splitting one optical signal into two parts, a semiconductor device, and a light receiving device. In the light splitting waveguide device, the waveguide portion is coupled with the optical fiber, and the semiconductor laser and the light receiving device are coupled after the light signal is split.
The light from the semiconductor laser is coupled with the light splitting waveguide device and advances along the waveguide and is coupled with the optical fiber the Y-shaped light splitting point and a common waveguide. The light inputted from the optical fiber is coupled with the common waveguide and advances and is split at the Y-shaped light splitting point. A part of the light advanced in the direction of the waveguide coupled with the light receiving device is coupled with the light receiving device for thereby detecting the light signal.
However, in this method, the semiconductor optical device and the optical fiber are coupled at both sides of the waveguide splitting device and then the light signal is split by the Y-shaped splitting point, so that a light advancing loss is decreased, and thus the light output and light receiving sensitivities are decreased. The devices are separately fabricated, and the optical coupling is implemented through an accurate optical alignment packaging process, so that the fabrication cost is increased, and it is impossible to fabricate a compact size product.
In order to overcome the problems that many parts and a multiprocess optical alignment packaging process are used, a method for integrating the semiconductor laser, light receiving device and light splitting waveguide device onto one substrate using a semiconductor process is disclosed. The integrated device has an excellent characteristic rather than when the devices are separately used. In addition, when aligning the optical fibers, it is possible to fabricate a desired waveguide for thereby simplifying the packaging process.
However, since the above-described method uses a light splitting waveguide, it is impossible to overcome the light loss and fabricate a small size product. In addition, since three kinds of optical devices having different structures and fabrication processes are integrated onto the identical semiconductor substrate as a single chip, it is very difficult to fabricate the integrated chip. In addition, it is impossible to obtain a high yield by optimizing the structure having a maximum characteristic.
There is another method for implementing a transmission and receiving operation of an optical signal having the identical wavelength using one optical fiber. In this method, a thin film filter surface has a 45.degree. inclination with respect to the axis of the optical fiber, and the semiconductor laser is installed behind the filter on the axis of the optical fiber, and the light receiving device is positioned at an by angle of 90.degree. with respect to the axial direction of the optical fiber above the filter.
The light from the semiconductor laser passes through the filter and is coupled with the optical fiber. In addition, the receiving light signal from the optical fiber is reflected at an angle of 90.degree. by the filter and is coupled with the light receiving device. In this case, the principle is simple but each optical device should be separately fabricated. The filter is bulky, and the packaging process for the filter and optical device alignment is complicated. The light coupling loss is increased because the light coupling distance is extended for thereby decreasing the light output and receiving strength.
In order to overcome the above-described problems, one optical fiber is used for thereby implementing a transmission and receiving operation instead of additionally using optical fiber, so that it is possible to decrease the fabrication cost of the optical fiber. Therefore, the number of parts is decreased, so that more economical optical communication is implemented. However, the system is made bulky and the number of parts is increased. In addition, it is difficult to fabricate a desired module. In the case when a single wavelength is used, an apparatus should be additionally used for eliminating any effects of the transmission and receiving light affecting the light receiving device. In order to be adaptable to the communication of a high density light wavelength splitting method, the optical device is separately fabricated, and the package structure is complicated for thereby increasing the fabrication cost.